1. Field of the Invention
The present invention relates to a film forwarding mechanism, and more particularly to a film forwarding mechanism having a reciprocating pawl to effect forwarding of successive units of film.
2. Description of the Prior Art
In a camera employing film in the form of individual units which are successively and independently developable by the so-called diffusion-transfer process effected by pressing means within the camera and then moved in the form of completed prints exterior of the camera, normally film units are initially contained in a pack which is loaded in the camera, and from which, at each successive exposure of a film unit, it is necessary to move the single exposed film unit and bring the film unit into engagement with processing rolls, for example, which are provided in the camera, but are exterior to the film pack, and apply pressure on the film unit to cause spread of a processing solution therethrough and development of the photographic image carried by the film unit, while the film unit is moved to the exterior of the camera, either by the processing rolls themselves or by other means. It has been known to effect such movement of a film unit entirely by manual means, for example by gear means actuable by a knob or knobs provided externally on the camera, or by a leader, or strip of paper, which is attached to the film unit and extends from the film pack to the exterior of the camera. However, such means have a main disadvantage that it is difficult to ensure that a film unit is moved through processing rolls at a required speed to ensure correct development of the image carried thereby, while there is also the inconvenience of difficulty of manipulation, and, if leaders are employed, of mounting a film pack in a camera. Accordingly it is generally preferred to effect such movement of a film unit automatically by means actuated in association with the camera shutter release means.
Conventionally, this automatic forwarding of film units may be effected by friction rolls which are provided in a camera in a position to contact successive film units to be forwarded from a film pack, to the processing rolls, or by a reciprocating pawl means which extends through a suitable slot formed in a film pack and may engage an edge portion of and draw out each successive exposed film unit. Film units being comparatively sensitive elements application of excessive pressure thereon is not permissible. Consequently, when friction rolls are employed to forward film units it is somewhat difficult to specify exact values of pressure to be applied by the rolls in order to ensure correct forwarding of film units but also avoid harm to photosensitive portions thereof, and since it is general practice to assign values of pressure including a safety margin to avoid harming film units, there may be problems of failure of friction rolls to forward film units completely out a pack. For this reason it is generally preferred to employ a film forwarding means comprising a reciprocally moveable pawl means, which engages comparatively strong edge portions only of film units and may always apply sufficient force to forward film units completely from a pack, such a pawl means being moved to a start position wherein it engages the edge portion of an exposed film unit, then moved in a straight line, simultaneously moving the exposed film unit out of the film pack, to an end position, the exposed film unit being brought into full engagement with processing rolls or similar means by the time the pawl means reaches the end position, and the pawl means being subsequently returned to the start position whereat it may engage an edge portion of the next film unit in the pack to be exposed. The drive for such a pawl means is conventionally a rotary drive, for example, by an electrical or spring motor provided in the camera, which is converted in a suitable manner to a linear drive, and stopping position of the rotary drive means must be accurately controlled, since otherwise there is a possibility of the pawl means forwarding two film units, one exposed and the second unexposed, in immediate succession from the film pack, or of the pawl means being prevented by the drive means from returning to the start position before being again moved to the end position, with the result that an exposed film unit fails to be forwarded. Such control is difficult, and if effected demands employment of precision means which are expensive.
It is accordingly an object of the invention to provide a film forwarding mechanism which is automatically actuated upon termination of a camera shutter release action.
It is another object of the invention to provide a film forwarding mechanism which comprises a moveable pawl element reciprocally moveable in a straight line for moving film forward in a required manner, and a rotary drive means for driving said pawl element, and ensures correct actuation of said pawl element but does not require provision of precision control means for controlling action of said drive means.
It is a further object to provide a film forwarding means having a simple and inexpensive construction.